The Couch/Linac Coordinate System; Overview - Brainlab EXACTRAC INFRARED MONITORING Clinical User Manual

4.2

The Couch/Linac Coordinate System

4.2.1

Overview

General To provide the ExacTrac patient positioning system with accurate information on the current patient
Information position, a three-dimensional coordinate system consistent with IEC 61217 is used to describe the
movement and angle of the couch and linac.
ExacTrac with
Linac
Axis Definitions
36
Axis
Point of origin (0,0,0)
Z-axis
X-axis
Y-axis
All numerical values displayed by ExacTrac Infrared Monitoring software are in milli-
meters [mm].
Z
Y
O
Figure 11
Function
This is the linac isocenter, and is defined by the intersection of the
gantry rotation axis with the couch rotation axis
This is the vertical axis that runs through the point of origin perpen-
dicular to the couch top plane at a tilt angle of 0°. Above the point of
origin this axis is positive, below the point of origin it is negative.
This is the horizontal axis that runs through the point of origin parallel
to the gantry rotation plane. When facing the linac from the foot of
the couch, this axis is positive to the right of the point of origin and
negative to the left. This axis is also known as the lateral axis, as it
describes the lateral movement of the couch.
This is the horizontal axis that runs through the point of origin parallel
to the couch top plane at a tilt angle of 0°. When facing the linac from
the foot of the couch, this axis is positive when moving towards the
linac from the point of origin, and negative when moving away from
the linac from the point of origin. This axis is also called the longitu-
dinal axis, as it describes the longitudinal movement of the couch.
Clinical User Guide Rev. 1.1, ExacTrac Infrared Monitoring Ver. 1.0
X
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